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Prof. Mridul M. Panditrao has added another of his very important, useful and in vogue topic to his collection. This is his well acclaimed andwell received faculty lecture at recently concluded International conference on Pain... ISSPCON 2014, at Mumbai/ Bombay from 6th to 9th Feb. 2014.

Modifications to LAAs • Mixing of the LAAs • Improving the pKa by trying to change pH: • Increase penetrability across the tissue planes/ neurilemma • Decreasing absorption/removal • Addition of various unrelated agents (non LAAs) to the mixture. • These are what we call “Adjuvants”.

ADJUVANTS? • Origin from French/ Latin; from Latin adjuvans, present participle of adjuvare - to aid or more at aid A pharmacological agent which is added to a drug to increase or aid its efficacy or one that helps or facilitates as: • a : an ingredient (as in a prescription or a solution) that modifies the action of the principal ingredient • b : something (as a drug or method) that enhances the effectiveness of medical treatment. Logically, anything which will increase efficacy and potency is an adjuvant! www.thefreedictionary.com/adjuvant, www.merriam-webster.com/dictionary/adjuvant

An “Ideal Adjuvant ?” There are certain characteristics/ properties which are desirable and needed in a drug, to be labelled as an “Ideal Adjuvant” • Physical • Pharmacological • Pharmacodynamic • Pharmacokinetic • Miscellaneous

An “Ideal Adjuvant” Pharmacological properties: Pharmacodynamics: • Enhance onset of action, • Maintain rapid and steady peak of action • Prolong the duration of action • Have no inherent, any other systemic effects/ side-effects • Not only enhance the efficacy of LAAs, but have its own inherent LAA like activity • Have a higher potency, so that requirement of dose is minimal • Should be completely devoid of any systemic toxicity

An “Ideal Adjuvant” Miscellaneous properties: • Should be economical • Should be freely available/ non-scheduled drug • Should not require any specific conditions for the storage Co-incidentally there is no single drug which can fulfill all these properties!!!!!!

ADJUVANTS Mechanisms of Action: • To decrease the uptake at the site of injection: • Change of pH/ pKa: • To Increase baricity: • To increase shelf life and sterility: • To form the water soluble complexes at the site: • To increase the penetrability across the tissue planes: • To prolong the duration of analgesia, both intra/ post-operative

5. To form the water soluble complexes at the site : Dextran To prolong the duration of action of the sensory blockade • Mechanism of action is not known: • dextrans may form water-soluble complexes with LAAs • remain at the site of injection longer than the unbound drug • due to an increase in viscosity with reduced diffusion of the complex • Alternatively, the addition of dextran makes more alkalinisation, which may contribute to the prolongation of action Conflicting results……. Fallen in serious disrepute/abandoned!!! •Aberg G, Friberger P, Sydnes G. Studies on the duration of local anaesthesia: a possible mechanism for the prolonging effect of dextran on the duration of infiltration anaesthesia. ActaPharmacologicaetToxicologica 1978; 42: 88–92. •Covino BG. Pharmacology of local anaesthetic agents. British Journal of Anaesthesia 1986; 58: 701–16.

6. To increase the penetrability across the tissue planes: Hyaluronidase • Especially in the peripheral, regional and superficial nerve blocks. • Nerves/ roots/trunks/ cords are enclosed in the fascial sheaths/ septae. • Transported across these structures for the better penetrability. • break the hyaluronic acid in the tissues • Increase the tissue permeability • Improve penetrability - Spread evenly and in the deeper plains • Dose of 7.5 IU/mL added to the local anesthetic improves peribulbar block15 •Kallio H, Paloheimo M, Maunuksela EL. Hyaluronidase as an adjuvant in bupivacaine-lidocaine mixture for retrobulbar/peribulbar block.AnesthAnalg. 2000;91(4):934-7.

7. To prolong the duration of peri-operative analgesia * • By acting at the one or all 4 important phenomena i. Transduction: By acting on nociceptors: peripheral, central ii. Transmission: By acting at the fibers: Aδ and C (periphery as well as near the neuraxis) iii. Modulation: By acting on neuromodulators iv. Perception: By acting at the central sites of perception. • *Mridul Panditrao. Pain and Its Physiological considerations. In Principles of Anaesthesia, Eds, Deshpande S et al. Paras, Hyderabad, India. 1st edition.2007:181-190

Conclusion • Quest for an “Ideal Local Anesthetic Agent” • The requirement of Adjuvants to LAAs is a real time ground reality and a challenging concept. • Almost every drug in an Anesthesiologists‟ armamentarium has a potential to be included in this group. • There is a need of imaginative planning, thorough execution and innovative analysis, while designing and carrying out various Randomized controlled Trials.

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